H.324 is an International Telecommunication Union (ITU) protocol standard for multimedia communication over general switched networks (GSTN). H.324M is an extension of H.324 for operations over mobile networks, and 3G-324M is a recommendation by the third generation partnership program (3GPP) defining adaptation of H.324M for use within 3GPP and also adopted by 3GPP2. We call H.324-like equipment devices and systems employing protocol based or derived from H.324. H.324-like equipment can connect to other H.324-like equipment via switching centers and to other non-H.324-like equipment through multimedia gateways. An example of a non-H.324-like equipment is an H.323 equipment. H.323 is an International Telecommunication Union protocol Standard for multimedia communication over non-guaranteed bandwidth packet networks. An H.323-like equipment is an equipment that employs a protocol based or derived from the H.323 protocol.
Without any loss of generality, we will use the term “H.324” to indicate H.324-like equipment including H.324M and 3G-324M equipment and “H.323” to indicate H.323-like equipment.
Also without any loss of generality we use the term “equipment” to indicate either a user end equipment such as a handset, or network end equipment such as a switch or gateway. The term “equipment” covers the meaning of “entity”. We also use the terms “equipment” and “terminal” interchangeably, and they both indicate the same meaning in the present document.
The present invention relates generally to the field of mobile networks. More particularly, the present invention relates to a method and apparatus for accelerated session setup in mobile networks. The method allows for the combination of a number of session setup techniques that can be used in a mobile terminal either together or independently of each other. Merely by way of example, three session setup techniques are combined in order to illustrate the operation of embodiments of the present invention.
If a call is made between equipments which are an embodiment of the H.324, H.324M or 3G-324M, the first stage of the call is to establish an end-to-end bearer between the equipments. This stage is called Call Signaling and is outside the scope of H.324, except where modems and the General Switched Telephony Network are used. The second stage of the call is to establish the H.324 session, to provide a means of transporting video, audio and data between the equipments in a format that is known to, and supported by the equipments.
We will refer to the time taken for information transmitted by one terminal to reach the other terminal and be reflected back in a response to the first terminal (see examples in FIG. 1) as a “round trip delay.” It should be noted that this round-trip delay assumes devices involved in the media processing and communication do not add delays and is intended to be a representative measure of the network delay.
The key steps involved in setting up and connecting a typical H.324 call are as follows:                1. Call signaling (bearer establishment)—outside the scope of H.324. Normally a modem connection if GSTN, through ISDN, or signaling through mobile switching centers in the mobile case.        2. Mobile level detection (MLD)—Where a common Mobile Level is agreed on between equipments. This step is performed by H.324 equipment that supports mobile extensions such as H.324M and 3G-324M equipment.        3. Terminal Capability Exchange (TCS)—H.245 Messaging        4. Master Slave determination (MSD)—H.245 Messaging        5. Open/Close Logical Channels (OLC)—H.245 Messaging        6. Multiplexer Table Entries Exchange (MTE)—H.245 Messaging        
Once these steps have completed, media (video, audio and data) can flow between the terminals.
The key steps above are often handled sequentially; as shown in FIG. 2, however this results in as many as ten H.245 message round trip delays in order to establish an H.324 session with two logical channels in each direction. Note in this case unidirectional video channels are used (e.g. video over adaptation layer AL2 of the H.223 multiplexer). In addition, the SRP scheme (or Numbered version—NSRP, in cases where the mobile level is greater than zero) used for H.324/H.245, which requires an SRP message to be received by the endpoint for every message sent, prior to sending any other message, regardless of whether it is associated with the same Signaling Entity or not, further limits the scope to pipeline messages on the network, making call setup slower than if this were not the case. SRP messages are not shown in FIG. 2.
In conventional equipment, the combined effect of the requirement to send an H.245 Response message for each H.245 Request Message received, and of the need to receive an SRP Ack for every SRP Command Frame sent means that a single H.245 Request message may take some time to be conveyed successfully. The communication involved in sending an H.245 Request message from one terminal (A) to another (B), and getting an H.245 Response (Ack) message back is shown in FIG. 1, which also shows the SRP Command Frames (SRP CF) and SRP Response Frames (SRP RF or SRP Ack) involved when single H.245 messages are formed into single SRP Command Frames.
Arising from the set of procedures described above that are required to take place to establish an H.324M call, when a call is made from a terminal which is an embodiment of the H.324 protocol it is prone to suffer from long call setup time, which is the interval between the time that the call signaling is initiated to the time that the exchange of voice and video commences between an H324-like end-point (H.324, H.324M or 3G-324M) and other terminals whether H.324-like or not.
Thus there exists a need for techniques to speed up the call setup between H.324 like terminals and other terminals (including servers) either of the H.324 type directly, or terminals such as H.323 via multimedia gateways that terminates the H.324 side and would have an H.324-like termination in them. The differences between the H.324 protocol (and its extensions such as H.324M and 3G-324M) and H.323 and other protocols mean that additional aspects need to be considered when introducing call establishment speed-up techniques for H.324-like terminals. Such differences include the information about mobile levels where they are used and the messaging and information related to the H.223 multiplexer such as its multiplex table entries, adaptation layers and so on. Also there is a tradeoff between characteristics, such as speed and flexibility that also must considered.